Sprayable portland cement-based fireproofing compositions

ABSTRACT

Sprayable fireproofing compositions for structural members such as steel columns are provided, as well as a method of applying multiple coatings thereof. The compositions comprise a Portland cement-based material, stucco, a high density aggregate and an accelerator. The compositions eliminate the long setting times typical of Portland cement-based materials, and improve the hangability thereof. The product is produced by dry blending a mixture of Portland cement, a high density aggreagte, stucco (calcium sulfate hemi-hydrate) and optionally, a stucco set retarder and shredded polystyrene aggregate. Upon the addition of water, sprayable slurries are formed which can be pumped to the point of application. An accelerator is added in close proximity to the point of injection. The slurries adhere to the structural member in the slurried state and after setting to provide excellent fire and heat protection. Because of the relative quick setting time of the slurry upon spray application, multiple coatings can be applied within the same working day.

This application is a continuation-in-part of Ser. No. 869,605, filedApr. 16, 1992, now U.S. Pat. No. 5,340,612.

FIELD OF THE INVENTION

The present invention relates to sprayable fireproofing compositions.

BACKGROUND OF THE INVENTION

It is well known to spray apply hydraulic cementitious slurries to metalstructural members in order to provide a heat resistant coating thereon.U.S. Pat. Nos. 3,719,513 and 3,839,059disclose gypsum-based formulationswhich contain, in addition to the gypsum binder, a lightweight inorganicaggregate such as vermiculite, a fibrous substance such as cellulose andan air entraining agent. Such slurries are generally prepared at groundlevel and are pumped to the point of application, where they are sprayapplied to the substrate. Often the point of application exceeds 20 or30 stories where high rise construction is involved. Accordingly,pumpability of the slurries is an important criteria in theirformulation and preparation. Thus, they must be able to hold the largequantity of water that renders them capable of being pumped easily andto great heights, yet they must retain a consistency sufficient toprevent segregation or settling of ingredients and permit adequate yieldor coverage of the substrate at a given thickness. The coating mixesmust adhere to the substrate both in the slurried state and in the drystate. Also, the mix must set without undue expansion or shrinkage whichcould result in the formation of cracks that would seriously deter fromthe insulative value of the dry coating.

U.S. Pat. No. 4,751,024, the disclosure of which is incorporated hereinby reference, teaches sprayable cementitious compositions containingshredded polystyrene as a lightweight aggregate in fireproofingcompositions. The cementitious binder is preferably gypsum, but mayinstead be Portland cement. Indeed, Portland cement is typically used asthe binder in applications involving high traffic areas, since thecement tends to be stronger than gypsum.

However, one problem associated with Portland cement-based fireproofingcompositions is the relatively poor hangability (the thickness ofmaterial that can be applied in a single application) thereof withrespect to gypsum-based compositions, since water tends to segregate inPortland cement mixtures in view of the relatively slow hydrationprocess. In addition, in view of the relatively long time it takes forPortland cement to set, only one spray application can be made per dayon a given substrate. Where the thickness of that spray application isinsufficient, a second application cannot be made until the firstapplication sets. Premature attempts to coat a second application resultin fall off. If multiple applications cannot be made in a typical eighthour work day, labor costs necessarily increase, as does the time inwhich a job can be completed.

Unlike gypsum-based compositions, which can be easily accelerated withalum, such as in close proximity to the spray nozzle as set forth inU.S. Pat. Nos. 4,904,503 and 4,934,596 (the disclosures of which areherein incorporated by reference), alum does not accelerate Portlandcement in sufficient time to allow multiple passes in one day. Inaddition, sodium aluminate should not be used as an accelerator, in viewof the corrosive nature of the sodium aluminate, which causes severecorrosion to the hot rolled steel substrates.

Accordingly, the fireproofing industry has long sought a Portlandcement-based sprayable fireproofing material that can be applied tosubstrates such as steel in multiple applications per day, and thatexhibits improved hangability notwithstanding such multipleapplications.

SUMMARY OF THE INVENTION

The problems of the prior art have been overcome by the instantinvention, which provides a sprayable fireproofing material whicheliminates the,aforementioned long setting times and improves thehangability of Portland cement-based compositions. In general, thesprayable fireproofing compositions of the instant invention comprise aPortland cement based material that is mixed with water in aconventional paddle mixer and is pumped through various types ofequipment. The material is spray applied onto steel beams and columns.The product is produced by dry blending a mixture of Portland cement,stucco (defined herein as calcium sulfate hemi-hydrate), and otheradditives, such as shredded expanded polystyrene, starch, adhesives andcement strength enhancers. Upon the addition of water, the drycompositions form pumpable, sprayable slurries. Preferably anaccelerator is added, most preferably in close proximity to the point ofinjection.

DETAILED DESCRIPTION OF THE INVENTION

The inventor of the present invention has found that causing a setacceleration of the Portland cement-based fireproofing enables multiplepass applications and improved hangability. That set acceleration can becaused by the addition of stucco, which can be sufficiently retarded toallow pumping and spraying, such as with a retarder, preferably aproteinaceous high strength retarder (commecially available from U.S.Gypsum), in an amount of about 0 to about 1.0% by weight of thecomposition, preferably about 0 to 0.6%. The amount of retarder mayvary, depending upon the particular cement and stucco being used. Theacceleration of the set is evidenced by initial quicker stiffening ofthe Portland cement/stucco matrix. The addition of aluminum sulfate,preferably in close proximity to the point of injection such as inaccordance with the method and apparatus disclosed in U.S. Pat. No.4,904,503 or U.S. Pat. No. 4,934,596 increases the speed of the settingprocess. This quicker set is sufficient to allow a second application ofmaterial to be sprayed in a few hours. In particular, when the Portlandcement/stucco formulation is injected with alum, the stucco sets, whichcauses a stiffening of the Portland cement matrix and quickens theincrease of the cohesive strength of the composition. Also, the settingof the stucco results in a quicker mechanical attachment to thesubstrate. This attachment is strong enough to allow a secondapplication without fall off within a period of eight hours, or oneworking day. The injection of alum in proximity to the point ofinjection enables quick setting of the material in a particular spot(i.e., on the substrate rather than in the hopper where the compositionis mixed).

The instant fireproofing compositions preferably contain shreddedexpanded polystyrene as an aggregate. The hangability of the instantcomposition may depend in part on minimizing the amount of non-shreddedexpanded polystyrene in the composition. The "shreddedness" of theexpanded polystyrene preferably conforms to a particular particle sizedistribution expressed in terms of the amount of particles retained on astandard #12 sieve (having 0.0661 inch holes), and the amount ofparticles passing through a standard #30 sieve and retained on a #325sieve, as determined in accordance with the method described in U.S.Pat. No. 4,989,464 (the disclosure of which is hereby incorporated byreference). Suitable amounts of particles retained on the #12 sieve,expressed as a weight percent, are from about 0 to about 20%, with fromabout 0 to about 10% being preferred. Suitable amounts of particlespassing through a #30 sieve (having 0.0234 inch holes) and retained on a#325 sieve (having 0.0017 inch holes) are less than about 40 % byweight, preferably less than about 30%.

Since the instant fireproofing compositions are typically transported tothe building site as dry mixtures, and are formed into slurries upon theaddition of an appropriate amount of water, the preparation andapplication processes may span many hours and thus the setting time ofthe mix is generally heavily retarded to provide an acceptable field potlife. This retarding in the mixer contradicts the desired quick settingtime upon spray application, and thus a delicate balance of retardingand accelerating is difficult to achieve. Obviously, were the mixture tostiffen substantially in the hopper, it would be rendered non-pumpableand therefore would be useless for the intended application. By addingretarder to the stucco, the retarded material does not stiffen asquickly in the mixer, and the retarder does not have any significanteffect on the quick stiffening at the nozzle. For these reasons, theaddition of retarder is preferred.

Any set accelerating agent capable of satisfactorily offsetting theretardation of the slurry without deleteriously effecting the slurry orthe substrate which is the subject of the application can be used.Preferably the accelerator is used in an amount sufficient tosufficiently set the slurry within 1.5 hours of spray application toallow for a second spray application without fall off. The particularamount required will depend upon the type of accelerator, as well as thenature of the various other components of the fireproofing composition.Examples of useful accelerators include aluminum sulfate, aluminumnitrate, ferric nitrate, ferric sulfate, potassium sulfate, sulfuricacid, sodium carbonate, sodium bicarbonate and acetic acid, with alumbeing especially preferred.

The present invention is applicable to Portland cement types 1 through5, although types 1 is especially preferred. The dry mix has a bulkdensity in the 10 to 65 pcf range, preferably in the 12 to 15 pcf rangefor low density mixes, and in the 30-55 pcf range for high densitymixes. The final dry density of the product is in the 15 to 65 pcfrange, preferably the 22 to 26 pcf range for low density products, andin the 40-50 pcf range for high density products. In the higher densityproduct, less Portland cement than in the lower density product is used(and therefore less water is used), and a high density aggregate such assand or bauxite or a mixture thereof is added. Any suitable grade ofsand may be used, as long as it does not deleteriously affect thehangability of the product or pumpability of the mix. Preferably thesame is oven dried. The preferred bauxite is hydrated and is a mixtureof coarse and fine grades. In addition, the amount of lightweightaggregate such as shredded polysytrene is decreased in the high densityproduct. The dry material is mixed with water at a ratio of 0.5:1-1.6:1(water:solids). A suitable product can be produced in accordance withthe invention by dry blending a mixture of the following:

    ______________________________________                                        Portland cement     30-90%                                                    Stucco               4-30%                                                    Retarder            0-1%                                                      Shredded polystyrene                                                                               0-5%,                                                                        preferably 2-3%                                           Clay                2-8%                                                      Cellulose (aggregate)                                                                             0-8%                                                      Air entrainment     0.2-2%                                                    Glass fibers        0-4%                                                      methyl cellulose    0-1%                                                      sand or bauxite      0-60%                                                    vinyl acetate       0-5%                                                      ______________________________________                                    

A preferred low density product includes the following range ofingredients:

    ______________________________________                                        Portland cement 67-74%                                                        Stucco          12-18%                                                        Retarder          0-0.6%                                                      Shredded polystyrene                                                                          2.5-3%,                                                       Clay (thickener)                                                                              2-6%                                                          Cellulose       2-6%                                                          Air entrainment 0.2-0.5%                                                      Glass fibers    1.5-3%                                                        methyl cellulose                                                                              0.2-0.5%                                                      biocide (Amical/wp sold                                                                       0.02 %, or an amount                                          by Angus Chemical)                                                                            sufficient to prevent deleterious                                             formation of bacteria                                         ______________________________________                                    

A preferred high density product includes the following range ofingredients:

    ______________________________________                                        Portland cement 40-50%                                                        Stucco          12-18%                                                        Retarder          0-0.6%                                                      Shredded polystyrene                                                                             0-1.5%,                                                    Clay (thickener)                                                                              2-6%                                                          Cellulose       2-6%                                                          Air entrainment 0.2-0.5%                                                      Glass fibers    1.5-3%                                                        methyl cellulose                                                                              0.2-0.5%                                                      biocide (Amical/wp sold                                                                       0.02%, or an amount                                           by Angus Chemical)                                                                            sufficient to prevent deleterious                                             formation of bacteria                                         sand or bauxite 40-55%                                                        vinyl acetate   1-3%                                                          ______________________________________                                    

Preferably the aluminum sulfate set accelerator is used as a 37%solution and is injected into the slurry at the spray nozzle at a levelup to 3%.

Additional optional ingredients may be added, such as glass fibers tocontrol shrinkage, methyl cellulose or other suitable thickeners knownto those skilled in the art, air entraining agents such as sodium laurylsulfate, and a biocide to inhibit bacterial formation.

In employing the fireproofing compositions in accordance with thepresent invention, a second application can be spray applied withinabout 1 to 2 hours, preferably within about 1.5 hours of the firstapplication without fall off. Improved hangability also resulted; asingle application typically could be spray applied to a thickness ofabout 3/4-1 inch, and was in fact spray applied to a thickness of asmuch as 1.5 inches, whereas conventional Portland cement-basedcompositions typically could be hung to thicknesses of only 1/2 to 5/8inches.

EXAMPLE 1

The following formulations were prepared:

    ______________________________________                                                            Nozl. Vicat                                               For-   %       %        Dry Bulk                                                                              (MM) @ 1 Hr                                   mulation                                                                             Stucco  Cement   Density Uninjected                                                                            Injected                              ______________________________________                                        Control                                                                               0      85.7     12.4    14.5    11.5                                  1       8      77.5     11.8    12      9.5                                   2      12      73.4     12.6    11      8.5                                   3      16      69.3     13.2    9.5     6.5                                   4      24      61.2     12.3    10.5    8                                     5      16      42.0     35.2    9.0     7.0                                   6      16      36.0     63.5    10.0    6.5                                   ______________________________________                                    

The cement in each of the above batches was type 1 Portland cement. Eachbatch was spray applied to a steel structural member, with 2.6% alumadded in accordance with the teachings of U.S. Pat. No. 4,904,503. The12% and 16% batches set sufficiently within 1 to 1.5 hours so that asecond application could be applied. The 12% and 16% first applicationhad a thickness of 3/4" to 7/8", with a total average thickness afterthe second application up to 1.5-2". With regard to the control, thefirst application amounted to a coating of up to 5/8 of an inch. Asecond pass (amounting to a total coating thickness of 1.5 inches) wasattempted after 1.5 hours, but fall off was encountered. In particular,the application of a second pass caused fall off of not only the secondapplication, but also some of the coating from a first application. Thissuggests that the coating of the first application did not sufficientlybond to the substrate within the 1.5 hour time period.

The vicat data is a measurement of the flow and stiffness of thematerial. The stiffness is generally an indication of how well the.product hangs. The lower the vicat reading, the stiffer the product.Preferably the vicar number is below about 10 mm, most preferably thereading is about 8 mm or less. Although the vicat reading of formulationnumber 4 in Example 1 seems excellent, in fact that formulation,containg 24% stucco, proved to be too stiff in the hopper; that is, theworkability was poor. In order to render such a formulation commericallyviable, additional water would have been necessary, thereby increasingthe final vicar number of the useable composition.

What is claimed is:
 1. A Portland cement-based sprayable fireproofingcomposition, comprising a dry blend of 30-90% Portland cement, 4-30%stucco, and a sufficient amount of a high density aggregate such thatsaid dry blend has a bulk density ranging from about 30 to about 55 pcf,and up to 3% of an accelerator for said Portland cement and stucco. 2.The sprayable fireproofing composition of claim 1, further comprising astucco set retarder.
 3. The sprayable fireproofing composition of claim1, further comprising shredded polystyrene.
 4. The sprayablefireproofing composition of claim 1, further comprising a high densityaggregate selected from the group consisting of sand, bauxite and amixture thereof.
 5. The sprayable fireproofing composition of claim 4,wherein said high density aggregate comprises 40-55% sand.
 6. Thesprayable fireproofing composition of claim 4, wherein said high densityaggregate is bauxite in an amount of 40-55%.
 7. A method of applyingmultiple coatings of a sprayable fireproofing composition to a steelsubstrate comprising dry blending a mixture comprising 30-90% Portlandcement, 4-30% stucco, and a sufficient amount of a high densityaggregate such that the resulting dry blend has a bulk density of 30-55pcf; adding water thereto to form a sprayable slurry; conveying saidslurry to a spray nozzle; introducing a set accelerating agent for saidPortland cement and stucco into said slurry before, during or after saidconveyance in close proximity to said nozzle; spraying a first coat ofsaid slurry onto said substrate; allowing said first coat to setsufficiently to hold a second coat; and spraying a second coat of saidslurry thereon within eight hours of spraying said first coat.
 8. Themethod of claim 7, wherein said dry blending step further comprisesadding a stucco retarder to said mixture.
 9. The method of claim 7,wherein said dry blending step further comprises adding a high densityaggregate selected from the group consisting of sand, bauxite and amixture thereof.
 10. The method of claim 7, further comprising a stuccoretarder, and wherein said stucco, retarder and accelerator are providedin an amount sufficient to allow said slurry upon application to saidsubstrate, to set within 1.5 hours.
 11. The method of claim 7, whereinsaid first coat of said slurry is spray applied to a thickness exceeding5/8 inches.
 12. The method of claim 7, wherein said first and secondcoats of said slurry have an average total thickness of about 1.5 to 2inches.
 13. The method of claim 7, where said dry blending step furthercomprises adding shredded polystyrene to said mixture.